1. Field of the Invention
The present invention relates to an antenna for a portable radiotelephone, and specifically to a means of switching between a transmitting/receiving main antenna element installed inside the case of the portable radiotelephone, from which the antenna may be freely withdrawn or re-inserted and a call signal-receiving sub-antenna element installed inside the case.
2. Prior Art
As is known, telephones are instruments which are used for two-way communication, and portable radiotelephones are also used in this way. In telephones it is absolutely impossible to predict when a call signal will be received from a calling party. Accordingly, in conventional portable radiotelephones, the antenna element is fixed so that it constantly projects outside the case of the portable radiotelephone to insure that a call signal can always be received. Thus, the antenna element projects from the case even when the radiotelephone is not in use. Accordingly, the antenna element may therefore create a nuisance.
FIG. 3 shows a conventional portable radiotelephone with a main transmitting and receiving antenna element 21 which can be freely inserted into or withdrawn from the case 20. When the radiotelephone is not in use, the main antenna element 21 can be accommodated inside the case 20. At the same time, a call signal receiving sub-antenna element 22 is installed inside the case 20. When the main antenna element 21 is inside the case 20, the sub-antenna element 22 is actuated by a change-over switch 23 linked to the inserting/withdrawing action of the main antenna element 21.
An antenna constructed as described above operates as follows: When the main antenna element 21 is located inside the case 20 as indicated by the broken line in FIG. 3, the change-over switch 23 is switched to side a by a driving means (not shown in the Figure) such as a spring. The switch 23 thus causes the sub-antenna element 22 to be connected to the transmitter-receiver set 24. When the main antenna element 21 is extended to the outside of the case 20 as indicated by the solid line in FIG. 3, an actuator 26 is pushed in the direction indicated by the dotted arrow in FIG. 3 by a projection 2 installed at the base end of the main antenna element 21, so that the change-over switch 23 is switched to side b. As a result, the main antenna element 21 is connected to the transmitter-receiver set 24.
An antenna assembly constructed as shown in FIG. 3 suffers two principal drawbacks: First, the system is constructed so that switching between the transmitting and receiving main antenna element 21 and the call signal-receiving sub-antenna element 22 is accomplished by means of a change-over switch 23 which has a mechanical contact. This conspicuously deteriorates to the antenna characteristics in a portable radiotelephone of this type (which uses ultrashort waves). Second, the changeover switch 23 is a square device occupying at least 1 to 3 cm.sup.3, a considerable amount of space. Furthermore, such a switch is expensive, tending to increase the overall cost of the radiotelephone.